Financial Instruments (Details 4) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Financial Instruments    
Restricted cash $ 2,824 $ 14,717
Due from related parties 10,597 14,459
Carrying value    
Financial Instruments    
Cash and cash equivalents 57,730 68,153
Restricted cash 2,824 14,717
Accounts receivable, net 7,904 8,038
Due from related parties 10,597 14,459
Receivable from ZIM   25,765
Equity investment in ZIM 28,693  
Accounts payable 12,510 13,124
Accrued liabilities 24,705 30,911
Long-term debt, including current portion 2,951,120 3,112,103
Vendor financing, including current portion 64,367 121,755
Carrying value | Unsecured 3% Series 1 ZIM Notes due 2023    
Financial Instruments    
Receivable from ZIM 6,274  
Carrying value | Unsecured 5% Series 2 ZIM Notes due 2023    
Financial Instruments    
Receivable from ZIM 30,923  
Total    
Financial Instruments    
Cash and cash equivalents 57,730 68,153
Restricted cash 2,824 14,717
Accounts receivable, net 7,904 8,038
Due from related parties 10,597 14,459
Receivable from ZIM   25,765
Equity investment in ZIM 32,873  
Accounts payable 12,510 13,124
Accrued liabilities 24,705 30,911
Long-term debt, including current portion 2,953,327 3,114,101
Vendor financing, including current portion 64,026 121,552
Total | Unsecured 3% Series 1 ZIM Notes due 2023    
Financial Instruments    
Receivable from ZIM 6,274  
Total | Unsecured 5% Series 2 ZIM Notes due 2023    
Financial Instruments    
Receivable from ZIM $ 30,923